Hemodialysis devices are known in various designs. The material exchange between the blood and the dialyzing fluid takes place in a dialyzer which has a first flow path for the blood and a second flow path for the dialyzing fluid, both flow paths being separated from each other by a semi-permeable membrane. The first flow path is a component of an extracorporeal blood circulation having a feed line and a return line for the blood, as well as, if desired, a pump supporting the blood flow. The second flow path is connected to devices for feeding and removing the dialyzing fluid. In addition to the so-called single-pass systems, in which the continually supplied dialyzing fluid passes the dialyzer only once and is then discarded, so-called batch systems are also known. The German Patent 31 15 665 C2 describes such a hemodialysis device which works with a volumetrically-fixed container, sealed off against the atmosphere, which is completely filled with fresh dialyzing fluid prior to beginning the treatment. During operation, fluid is pumped out of the container through the dialyzer, and the used fluid is fed back into the container again. Because of the constant volume of the entire system filled with the dialyzing fluid, ultra-filtration can only be carried out when fluid is removed from the system. A mixture of fresh and used dialyzing fluid is avoided in the known hemodialysis device, in that the removal of the dialyzing fluid is carried out in the upper region of the container, while the feedback takes place in the lower container region. The stratification of the fresh dialyzing fluid with the used dialyzing fluid remains stable due to the maintenance of a vertical temperature gradient in the container from top to bottom.
The container is made of glass which is substantially resistant to chemicals to be considered, cleans well and is physiologically unobjectionable. However, it is disadvantageous that the glass container is comparatively costly to produce and relatively difficult to clean.
The German Patent 198 25 158 C1 describes a disposable, constructed as a film bag, which, together with a shaping vessel, is able to replace the glass container, relatively expensive to produce, of the hemodialysis device which is described in DE 31 15 665 C2 mentioned at the outset. The disposable is made of two twisted-conical sections which are welded together at their peripheral edge to form a double cone. The special advantage of this form design is that the disposable can be produced from conventional (flat) films. A three-dimensional fashioning as, for example, in the case of disposable gloves, is not necessary for this.
The glass container can only be replaced by the film bag if the volumetric constancy, sterility and fluid stratification are guaranteed.
To ensure the volumetric constancy, the bag must be able to unfold reproducibly and completely in the pressure-stable vessel with defined volume while being filled. Air pockets between bag and vessel, which develop due to unfoldings or spaces to be bridged, must be largely avoided. Creases caused by the geometry can only be accepted if they are reproducible, and the volume enclosed by them is negligible compared to the total volume. To ensure sterility, the interior of the bag must not be opened during the dialysis preparation, and during the filling, should only come in contact with the fluid flowing in. For the fluid stratification, the shape of the bag must support a clear separation between fresh and used dialyzing fluid. In addition, the bag should be easy to handle and inexpensive to produce.
French Patent publication no. FR 2 749 763 describes a method for producing a salt concentrate for the hemodialysis. The salt concentrate is made available in a bag which is folded from a tubular film. It is a side-fold bag which is able to unfold to form a rectangular packet.
The U.S. Pat. No. 5,607,082 describes a tank for a compression sprayer having an outer container which accommodates an inner container. The inner container has a rigid back wall and is folded like a concertina.
From DE 9417416 U1, a secretion-collecting bag is known which is able to fold together like a concertina.